Doctoral Degrees (Mechanical and Mechatronic Engineering)

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Browsing Doctoral Degrees (Mechanical and Mechatronic Engineering) by browse.metadata.advisor "Dinter, Frank"

Now showing 1 - 5 of 5
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    Development of a micro-gas turbine for central receiver concentrating solar power systems
    (Stellenbosch : Stellenbosch University., 2020-03) Ssebabi, Brian; Van der Spuy, Johan; Dinter, Frank; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: There is limited access to electricity in much of Southern Africa, yet this region receives some of the highest solar irradiation worldwide. Consequently, there is a huge potential for the deployment of concentrating solar power (CSP) distributed electricity generation systems. The application of gas turbines in central receiver CSP systems combines high concentration ratios of central receiver technology and the ability to scale in size, with inherent gas turbine advantages. This makes these systems ideal for distributed electricity generation applications. However, there are currently no commercial solar-hybrid gas turbine systems readily available off-the-shelf. Through both a theoretical and experimental approach, this study therefore aims to develop a micro gas turbine (MGT) system for central receiver CSP distributed electricity generation applications. The theoretical work involved modeling the performance of a MGT system under solar-hybrid operation, in order to predict the possible operating range and develop suitable operation and control strategies for the MGT system. The experimental work involved designing, building, testing and characterising the performance of an experimental MGT system and then using the obtained test data to validate the predicted performance, as well as assess the technical feasibility of adapting such a system to solar-hybrid operation. The component matching showed a shift of the equilibrium running point on the compressor characteristic, to counter the additional system pressure losses and ensure a useful work output, albeit with a reduced surge margin. Solar-hybrid operation was only possible for a solar share of at least 20 %, while the work output and cycle thermal efficiency drop below standard operation levels beyond certain solar share. In contrast to standard operation, a higher nominal work output of 20 kW, at a lower specific fuel consumption of 0.0004 kg/kWh and a higher cycle thermal efficiency of 8 % was predicted, the latter potentially increasing to 20 % with recuperation. Based on the proposed control strategy of operating the MGT system at the determined solar-hybrid equilibrium running point, sudden changes in solar irradiation were corrected by altering the fuel flow. From the validation of the predicted performance, the predicted MGT system equilibrium running point matched the optimum experimental equilibrium running points, and a similar shift on the compressor characteristic was predicted for varying levels of system pressure losses. The use of turbocharger technology should allow for easy coupling of the individual MGT system components, some of which could be specially designed for solar-hybrid operation. The twin-shaft configuration allows for flexibility in operation, with the added advantage of ease of starting. The large swallowing capacity of the much bigger power turbine should further ensure that the MGT system is insensitive to load variation. The findings from this study should guide operation and control strategies for the proposed, and future solar-hybrid MGT systems, which should in turn contribute to their development and commercialization.
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    Optical performance of the reflective surface profile of a Heliostat
    (Stellenbosch : Stellenbosch University, 2017-03) Landman, Willem Adolph; Dinter, Frank; Gauche, P.; Stellenbosch University. Faculty of Engineering. Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Micro gas turbine (MGT) central receiver systems offer advantages which could improve the techno-economic viability of the next generation of concentrating solar power (CSP) plants. This relatively young technology is not yet well understood, and the optimal configurations are yet to be determined. The high flux requirements and small modular configuration suggest that the heliostat field of a MGT CSP plant may have alternative parameter sensitivities than conventional systems. The objective of this thesis is to fundamentally understand the optics of a heliostat to develop methods, models and figures of merit as tools to improve the techno-economic viability of central receiver systems with particular emphasis on MGT CSP. A study of the fundamentals of heliostat optics shows that heliostat beam aberrations are statistically differentiated according to whether they occur consecutively or are path dependent. Three key factors – namely the sun shape, normal vector error aberrations and astigmatic aberrations – are found to dominate the dispersion of a heliostat beam and they are described analytically. This knowledge presents the principal components required to accurately describe heliostat field performance. The development and validation of a new analytical method to model flux distribution of a heliostat shows that it is possible to achieve suitable levels of confidence by appropriately accounting for these factors. The accuracy improvements offered by the method is particularly beneficial when used to model higher accuracy heliostats that would typically be used in MGT CSP. The flux distribution error and peak flux error of the proposed method are shown to be up to 60.6% and 88.2% lower than that of state of the art methods respectively. This method is applied in a techno-economic sensitivity study that illustrates that high accuracy optics result in lower levelised cost of energy. Both the cost breakdown and the alternative optical requirements show that MGT CSP does have alternative parameter sensitivities. The collective findings of this thesis suggests that small heliostats offer significant optical performance increases in the context of MGT CSP and potentially leads to cost minimum.
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    Optimisation in plant operations for a 100 MW Central Receiver CSP plant with focus on the plant operating strategies.
    (Stellenbosch : Stellenbosch University, 2018-03) De Meyer, Oelof Abraham Jakobus; Dinter, Frank; Govender, Saneshan; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: As South Africa progresses towards a more diverse energy mix, it is essential to comprehend both the contribution and implications that renewable energy generating technologies have on the electric grid. Therefore, this dissertation emanated from Eskom’s directive aims to acquire a comprehensive understanding of the technical, financial, and operational aspects of running a plant that is built on concentrating solar central receiver technology. Independent Power Producers (IPPs) and Concentrated Solar Power (CSP) plant operators across the globe predominantly adopt the Maximise Power Generation operating strategy. It is necessary to determine the means to optimise the plant operations as a varying operating strategy is envisioned for the plant. Therefore, this research investigated the effects of an array of varying operating strategies imposed upon the plant, which is an essential exercise to determine the possible role of CSP within the South African electric grid. Three boundary conditions determine the operations of a CSP plant: weather conditions; plant status; and operating strategy. After an extensive literature review, it is established that no publically available model is available to optimise the plant operations under the aforementioned conditions. Therefore, a simulation model was developed in the current research to optimise the plant under these boundary conditions. The basic design of Eskom’s 100 MW CSP project was used as the reference plant in developing the simulation model. Subsequently, the simulation results and performance curves of each subsystem within the plant, i.e. the heliostat field, receiver and power block, are validated against other commercially available simulation models. The operational logic is implemented in the validated model to objectively simulate the plant operations considering the specified boundary conditions. The developed simulation model successfully demonstrated through simulation the effects that (i) weather conditions, (ii) plant status and (iii) operating strategies have on both, the plant performance and operational capabilities of the central receiver technology. The advantages that this model offers over the other similar simulation models available in literature are as follows: provides a detailed, up to seven-day forecast, of the plant operations; implements time resolution of 15 minutes increasing the transients and results accuracy; provides user flexibility to specify the precise boundary conditions imposed on plant operations; offers capability of comparing various simulations or operating strategies by providing key performance and financial indicators. The dissertation and developed model offers Eskom and the system operator with the required tools to address the specific business needs, also identified by the Eskom Power Plant Engineering Institute (EPPEI) program. The resulting cost of generation, performance indicators and operational capabilities demonstrated are to assist in future Power Purchase Agreements (PPA) and national policy formulations.
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    Solar thermal treatment of manganese ores
    (Stellenbosch : Stellenbosch University, 2023-03) Hockaday, Aletta Carolina; Dinter, Frank; McGregor, Craig; Reynolds, Quinn; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH SUMMARY: The use of sunlight as an alternative energy source is well established in the electricity sector, but mineral processing has lagged in adopting renewable energy sources. Specifically, the combustion of fossil fuels for process heat and using coal as a reductant are still the norm. It is possible to heat minerals directly with concentrating solar technology. Simultaneously, thermal decomposition reactions can cause the removal of oxygen or the decomposition of carbonate minerals without reductants. The use of concentrating solar technology for the pre-treatment of manganese ores was investigated in this light. Pre-heating, calcination and pre-reduction were identified as processes within the temperature range achievable by solar particle receivers. Manganese ores differ in the amount of carbonate minerals present and in the degree of oxidation of manganese. After chemical and mineralogical assaying of three South African manganese ores, their behaviour was investigated in thermogravimetric laboratory experiments. Tests were also done using a rooftop flat mirror parabolic dish concentrator to confirm that the laboratory studies may be used to inform the ores’ behaviour in on-sun conditions. Comparing the mass loss achieved during experiments to expected mass loss under equilibrium conditions, it was clear that mass loss was kinetically limited at temperatures below 950 °C. A dynamic reaction rate model was formulated from published literature to explain the ore behaviour in this temperature range. The model was validated against the measured mass loss data from all the experiments. Scaling of the technology was investigated for a 2.5 MWt solar plant. A radiation view factor model was formulated describing the rotary solar receiver energy flows. The reaction rate model was incorporated into this dynamic process model, enabling the calculation of the material composition in each receiver zone and for the products. The model was evaluated for daily and monthly periods in minute timesteps. The products were shown to produce energy savings and reduce greenhouse gas emissions when used in high-carbon ferromanganese production. The solar thermal plant process model showed that a 2.5 MWt solar plant can treat 5800 to 10600 metric tons of manganese ore per year at a levelised cost of heat of 380 R/MWh for 20-year project life. At the same time, while avoiding greenhouse gas emissions, this energy cost is lower than that of electric heating and heating with diesel combustion.
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    A Technical and economic assessment of molten salt parabolic trough power plants and operating strategies in Southern Africa.
    (Stellenbosch : Stellenbosch University, 2020-12) Pan, Christoph Adrian; Dinter, Frank; Harms, T. M.; Van der Spuy, S. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Parabolic trough power plants (PTPP) using thermal oils as heat transfer fluid (HTF) are currently still state-of-the-art. Using molten salts as HTF instead enables higher operating temperature differences and therefore higher cycle efficiencies. Nevertheless, the use of molten salts is linked to several engineering and operational challenges that require special consideration to be placed on improved operating strategies and power plant configurations. This can, for example, be achieved through a technical and economic assessment,where design variables and operational parameters can be determined that lead to an optimised financial feasibility of molten salt PTPPs for various operating objectives.For this purpose, a two-dimensional dynamic parabolic trough solar collec-tor model using molten as HTF was developed and validated with measure-ment data obtained from the Archimede Solar Energy demonstration plant formolten salt receiver tubes in Massa Martana, Italy. An empirical heat loss equation based on the outer surface temperature of the absorber tube was introduced to the model in order to improve simulation efficiency. The finite volume method was applied to discretise the receiver into control volumes,whereby the effect of decreasing levels of discretisation on the model accuracy is analyzed. The relative error of the loop outlet temperature is 0.69 % for the most detailed model and 0.99 % when one control volume per solar collector array is used. A division into five control volumes is recommended as a trade-off between model accuracy and simulation time. A location-tailored economic model for South Africa and Namibia was implemented and validated with financial data of two existing concentrating solar power plants in South Africa, leading to a maximum error of−5 % for the levelised cost of electricity (LCOE). A sensitivity analysis was carried out to identify the key technical and financial design parameters that lead to the best potential improvements in terms of power plant efficiency and profitability. In order to combine the cost reduction potentials of all key design parameters identified in the sensitivity analysis, a multi-objective optimisation was carried out, simultaneously minimising the investment costs and maximising the internal rate of return. The results show that Solar Salt offers the lowest LCOE out of three investigated HTFs and a freeze protection system using thermal energy from the hot tank enables a significant reduction of the LCOE in comparison to the baseline approach of relying on electric freeze protection only. Based on the optimisation results, a range of power plant configurations and operational parameter set points are recommended for base load and two-tier tariff structures. For base load power plants, the minimum required bidding tariff is 119.4 $/MWh in South Africa and 115.8 $/MWh in Namibia under cur-rent financial boundary conditions. A projection of the LCOE until 2050 showsthat an LCOE of 49.6 $/MWh is expected for South Africa and 49.3 $/MWhfor Namibia with a technology learning rate of 20 %. However, assuming reduced financing costs, tariffs as low as 50.4 $/MWh can already be financially feasible today and a spot market participation of molten salt PTPPs is possible with LCOEs between 58.9 $/MWh and 65.6 $/MWh.